It is known in medium to heavy duty punching units to use various type punch and die supporters. In C-frame holders, for example, there are several units for punching holes in material or workpieces from about 3/4 inch to 1 inch thick. Since the workpieces used are comparatively thick, after continuous usage, the C-frame tooling begins to become deflected or offset structurally. When this occurs the holes punched using that particular C-frame equipment become off-centered and non-uniform. Conversely, if the C-frame tooling is somewhat deflected or deformed because of heavy use, the stripper plate and punch used therewith may also deviate from the vertical and horizontal and thus may act upon the workpiece non-uniformly. In addition, after constant usage, the punch because of less than continuous support can become offset and become deflected. This will result in off center holes being imparted into the workpiece. Also, because of a lack of total vertical support, the punch after continuous usage may become irregularly worn and must be frequently replaced. When the punch is worn in an irregular fashion, the holes and resulting slugs therefrom are not as precise or sharp as they should be or as precise as they were when the punch was new and not worn. There is a need for a device that provides substantially continuous vertical support for the punch and punch housing. A structure that reduces shock, deflection of the punch, deflection of the C-frame tooling areas, reduces wear on the punch and reduces the operational noise level would be a major contribution to the art.
There have been several attempts to strengthen the arms of a C-frame holder or tooling. One method that has been attempted to strengthen the upper arm of the C-frame holder is to install support bars on either side of the arm and thereby minimize the deflection of this arm due to structural pressure caused by constant heavy usage. This method has not been successful and upper arm deflection continues to be a problem. As noted earlier, the upper arm supports the punching assembly containing the punch and, if the upper arm is off kilter, all elements supported thereon will be equally off kilter including the punch. This results in holes of various tolerances being imparted in subsequent worked workpieces. Various type workpieces may be used such as metal, plastics, paper goods, fiberglass, and any other suitable materials.
Another corrective measure attempted by the prior art has been to suspend and project metal screws or pins down from the upper arm and up from the lower arm of the C-frame. These pins minimize the gap between the C-frame arms and provide means for supporting a workpiece during the punching operation. While these screw supports or guides have somewhat reduced upper arm deflection of the C-frames, they also became deformed during usage and have not provided a satisfactory solution to this problem.
C-frame structures of the type disclosed in U.S. Pat. Nos. 2,758,560 and 3,461,762 and those illustrated in a catalog published by Unittool Punch & Die Co., Inc. of P.O. Box 863, Buffalo, N.Y. Catalog H-85 are illustrative of the structures that can experience these problems. Obviously, any suitable type holder for punch and die units may be used with the device of the present invention. Therefore, while the present invention will be illustrated as installed in C-frame holders, it is to be understood that the novel unit of this invention has utility in any other suitable type holder.
In the prior art units the punch plate has attached thereto in approximately the center of said plate a punch housing. Inside the punch housing is secured the punch which will impart the desired hole configuration in a workpiece. On either side of the punch housing are stripper springs that provide downward movement to the punch and punch housing when a pressure is exerted upon the punch plate. The springs and punch housing are suspended from and attached to the punch plate. Below the springs and attached thereto is a stripper plate having a central aperture therein through which the punch and punch housing project when making contact with a workpiece during the piercing or punching operation. This aperture is substantially larger than the dimensions of the punch and punch housing and will allow the punch side to side movement during the piercing operation. It is this lateral movement from the vertical axis of the punch that causes in the prior art irregular wear on the punch and eventually deflection and deformation of the upper arm of the C-frame holder which supports the punch housing. Part of this prior art problem is caused because of the large gap between the arms of the C-frame holder and the lack of vertical support for the punch when it impacts upon the workpiece. Also, in the prior art, because of side loading, galling of the workpiece occurs and the punch becomes dull and non-uniform. Without adequate support the punch will chatter and wobble during usage, will make a rapid clicking noise and will vibrate somewhat so as to produce flaws or defects or non-uniformity in the workpiece.